1. Field of the Invention
The present invention relates, in general, to a cooling device for halogen lamps in microwave ovens and, more particularly, to a cooling device designed to expose the sealing parts of a halogen lamp to a cooling air current.
2. Description of the Prior Art
As well known to those skilled in the art, a variety of cooking devices have been proposed and used. Of the cooking devices, the primary one is cooking ware, which is designed to have a shape suitable for containing food therein and is laid on a heater so as to be directly heated by the heater while cooking.
In addition, several types of electric cooking devices, designed to directly or indirectly utilize electric power while cooking, have been proposed and used. An example of conventional electric cooking devices is a microwave oven using a magnetron as a heat source. In such a microwave oven, the magnetron is electrically operated to generate microwaves and applies the microwaves to food in a cavity, thus allowing the microwaves to cause an active molecular motion in the food. Such an active molecular motion in the food generates molecular kinetic energy, thus heating and cooking the food. Such microwave ovens are advantageous in that they have a simple construction and are convenient to a user while cooking, and easily and simply heat food in the cavity. The microwave ovens are thus somewhat preferably used for some cooking applications, such as a thawing operation for frozen food or a heating operation for milk requiring to be heated to a desired temperature.
However, such microwave ovens also have the following problems. That is, the ovens have a defect in their heating style in addition to limited output power of the magnetron, and so it is almost impossible to freely or preferably use them for a variety of cooking applications, without limitation. In a detailed description, the conventional microwave ovens only utilize a magnetron as a heat source, thus undesirably having a single heating style. In addition, the output power of the magnetron, installed in such ovens, is limited to a predetermined level. Therefore, the conventional microwave ovens fail to provide a quick and highly effective cooking operation. During a cooking operation utilizing such a microwave oven, food in a cavity is heated at its internal and external portions at the same time, and this may be an advantage of the oven in some cases. However, such a heating style may result in a disadvantage while cooking some food. For example, the cooking style of the conventional microwave ovens is not suitable for cooking pizza for reasons that will be described in more detail later herein. Another disadvantage, experienced in the conventional microwave ovens, resides in that the ovens exceedingly remove moisture from food.
In an effort to overcome the above-mentioned problems, several types of microwave ovens, having another heat source in addition to a magnetron, have been proposed and used. For example, a microwave oven, having a convection heater in addition to a magnetron in a casing and originally designed to be used for a variety of cooking applications, has been proposed. However, such a convection heater only acts as a single heat source, thus failing to allow the microwave oven to have a variety of operational functions.
In a brief description, the conventional microwave ovens are problematic in that they have a single heating style utilizing microwaves, limited output power of a magnetron, and cause the evaporation of an exceeding amount of moisture from food. The microwave ovens, having another heater in addition to a magnetron, fail to completely overcome the problems experienced in the conventional microwave ovens.
In order to solve the problems of the conventional microwave ovens, another type of microwave oven, utilizing a light wave, has been proposed. In this microwave oven, a lamp, wherein at least 90% of the radiation energy has a wavelength of not longer than 1 .mu.m, is used as the additional heat source. In said microwave oven, both visible rays and infrared rays from the lamp are appropriately used, and it is possible to preferably heat the exterior and interior of food while making the most of characteristics of the food. An example of such a lamp is a halogen lamp.
Due to a difference in wavelengths between the infrared rays and visible rays emanating from a halogen lamp, the heating styles for the exterior and interior of food are different from each other. While cooking pizza utilizing a halogen lamp, it is possible to appropriately heat the pizza in a way such that the exterior of the pizza is heated to become crisp and the interior is heated to be soft while maintaining appropriate moisture.
FIG. 1 is a conventional microwave oven utilizing a halogen lamp as an additional heat source. As shown in the drawing, the microwave oven comprises a halogen lamp 12 installed on the top wall 10 of a cavity 2. The microwave oven uses the light waves, radiated from the lamp 12, for heating food in the same manner as that described above, with the characteristics of the light waves remaining the same as that described above.
A light reflection plate 14 is installed at a position above the halogen lamp 12, thus reflecting any light waves, emanating upwardly from the lamp 12, back downwardly into the cavity 2. A plurality of light transmitting holes 16 are formed on the top wall of the cavity 2, with the halogen lamp 12 being held on the top wall. The structure for holding the halogen lamp 12 within the reflection plate 14 is shown in FIGS. 2 and 3. As shown in the drawings, the reflection plate 14, surrounding the halogen lamp 12, is closed by a support member 18 at each end thereof. The support member 18 is also used for supporting each end of the lamp 12. The halogen lamp 12 has a sealing part 12a at each end thereof. At the sealing part 12a, an external lead wire 17 is connected to an internal filament 12b of the lamp 12. An electric insulator part 12c, made of a ceramic material, is provided on each end of the lamp 12 at a position outside the sealing part 12a.
Since the halogen lamp 12 generates a great quantity of light waves during an operation of the microwave oven, the lamp 12 is heated to a high temperature during an operation of the microwave oven. In addition, when the interior equipment of the microwave oven is overheated, there may occur safety hazards, such as fire, in the microwave oven. Therefore, it is necessary to cool the interior equipment, such as the halogen lamp 12, to an acceptable temperature of not higher than a reference point. For example, it is necessary to cool the halogen lamp 12 to a temperature of not higher than 800.degree. C. and to cool the sealing part 12a to a temperature of not higher than 300.degree. C. However, the sealing part 12a of the halogen lamp 12 is apt to be undesirably overheated during an operation of the microwave oven.
The conventional structure for holding the halogen lamp 12 relative to the light reflection plate 14 is designed as follows.
As shown in FIGS. 2 and 3, the two electric insulator parts 12c of the halogen lamp 12 are held by the two support members 18. This is caused by the fact that it is easier and more effective to hold the lamp 12 on the members 18 at the insulator parts 12c. Such a holding structure renders the two sealing parts 12a to be positioned within the light reflection plate 14. In FIG. 3, the reference numeral 22 denotes a mesh member used for guiding the heating light from the lamp 12 into the cavity 2. The reference numeral 24 denotes a lamp protection filter used for protecting the lamp 12 from the steam and oil smoke laden with impurities rising from food during a cooking operation.
A cooling fan unit (not shown) is installed within the microwave oven so as to cool the halogen lamp 12. The above cooling fan unit generates a cooling air current that is mainly used for cooling the lamp 12. As well known to those skilled in the art, the parts of the halogen lamp 12, which most require cooling, are the sealing parts 12a. However, since the sealing parts 12a are positioned within the reflection plate 14 and are covered with the support members 18 in the conventional structure, the sealing parts 12a fail to be effectively cooled to a desired temperature.
When the halogen lamp 12 is turned on and radiates the heating light, the interior of the reflection plate 14 is further heated to a higher temperature. In this regard, it is a very important factor to effectively cool the sealing parts 12a to a desired temperature. When the sealing parts 12a fail to be effectively cooled, the expected life span of the lamp 12 is undesirably shortened. This results in a reduction in the operational reliability and market competitiveness of the microwave ovens.